The oil and gas industry has been continually drilling wells deeper and deeper into extremely high underground pressure areas or zones, which zones many times contain hostile and corrosive chemicals such as hydrogen sulfide. To complete a well for oil and/or gas production normally requires cementing casing in the well hole to prevent cave-ins and other phenomenon both during and after the drilling operation. Once the casing is positioned within the well hole, tubular pipes of reduced diameter, commonly known as tubing, are positioned within the well casing and extend the full length thereof for effectively carrying the hydrocarbons and gases contained within the production formation to the surface. These tubular pipes or tubing are manufactured by steel mills in average lengths of approximately 30 to 40 feet and therefore must be connected or joined together as they are lowered into the well by means of mechanical connector devices. Connectors for the tight joinder of such well tubing are well known in the petroleum industry. These connectors perform many functions but their primary function is essentially twofold, namely, (1) to adequately hold the string of pipes together within the well hole and (2) to adequately seal the connected together tubular members against the internal and/or external pressures commonly associated with drilling for and pumping oil and/or gas. Hereinbefore, pressure seals were simply created by interference fit of the male and female threads associated with the respective tubing to be joined. Such joinder means generally comprises a male extremity or pin associated with one tube element and a female extremity or box associated with the other tube element, each of which is respectively fitted with corresponding threads such that when the male extremity is threadingly positioned into the female extremity, the locking of said threads occurs. This joinder method became inadequate for many wells when well depths reached approximately 10,000 feet due primarily to the higher pressures associated with the oil and gas formations found at such depths. These related higher pressures have therefore produced a need for connectors or connecting means having a pressure sealing ability capable of adequately withstanding both the internal and external pressures associated with such well depths.
Metal-to-metal pressure seals were first successfully introduced into the oil and gas industry by the Hydril Company based upon Stone U.S. Pat. No. 2,006,520. The seal disclosed in the Stone patent was based upon a wedged fit between a seal surface on the male extremity or pin and a corresponding seal surface associated with the female extremity or box, which surfaces engaged just prior to shouldering. Although this sealing arrangement provides an effective seal, it functions without any back-up sealing means in case of failure, a feature necessary for maximum sealing integrity in today's deep well environment. In addition, the sealing arrangement of Stone is also very susceptible to handling damage due to its location on the connector. If the seal element surfaces are even slightly scratched or otherwise damaged, the seal will not seat properly and the gas and/or oil pressures generated during drilling and pumping operations will easily move past the seal area and into the connector body where such pressure will eventually or immediately cause failure. Long term storage of the known prior art connectors also causes problems in that such storage causes the sealing surfaces to deteriorate due to pitting and other corrosion, all of which cause deterioration of the sealing capability of the connector. Such failures cannot be tolerated not only because they are very expensive but also, and more importantly, because they are extremely dangerous to the lives of those working in the area of the well.
A successful incorporation of two adjacent metal seals in a coupling device was marketed by Vallourec Steel and is disclosed in Duret U.S. Pat. No. 3,489,437. This sealing arrangement has been fairly successful except that, again, it is highly susceptible to damage during normal field handling and during running operations. For example, if the double seal surfaces of Duret are even slightly dented, nicked, or galled prior to make-up of the connention, such defects will cause the pressure seals formed by the mating of said seal surfaces to deteriorate and the associated pressures will again migrate through the seal area causing leakage and/or joint failure. In addition, the Duret sealing configuration is extremely sensitive to leakage and/or failure due to the sharpness of the angles of the seal element surfaces relative to the longitudinal axis of the pipe. For example, if any foreign matter, no matter how small, is trapped between the seal surfaces during make-up, the respective seals will not seat properly and therefore will not provide an adequate pressure seal. Because of its sensitivity and suspectibility to improper seating due to damage caused during field handling, stabbing, and other phases of a drilling operation, this sealing arrangement is not widely utilized in the United States.
It rapidly became apparent that back-up seal elements were necessary for insurance against pressure leaks and the often resulting connector failures associated therewith. Many independent sealing devices such as rings and gaskets have been utilized as both back-up and primary seals. The two most effective seals in use today utilize teflon seal elements trapped or at least partially trapped in the joinder connection so as to block any pressure from migrating therethrough. These seals were marketed by Atlas Bradford of N. L. Industries, Inc. and are disclosed in Taylor U.S. Pat. No. 2,980,451 and Wehring U.S. Pat. No. 3,047,316. These sealing rings and/or gaskets have served well as back-up sealing elements. However, the effectiveness of such sealing means has deteriorated within the last ten years due to the fact that oil and gas well drillings have reached well depths far beyond 10,000 feet and, in addition, drilling to such depths has exposed the well tubing and its connections to many corrosive elements such as hydrogen sulfide. As a result, seal failures have also occurred due to the corrosive effect of hydrogen sulfide. Most hydrogen sulfide failures are associated with high stress levels in the metal connectors. The teflon seal rings generate very high stress levels during make-up of the connection in order to obtain an adequate pressure sealing barrier and therefore are highly susceptible to such corrosive failure. In addition, replacement of one or more defective sealing rings is extremely time consuming and costly since the defective portion of the string of pipe must be tripped out of and then back into the well hole. This problem is accented in the international marketplace where stocking of replacement parts is always a problem and very expensive.
Consequently, no known joinder means utilized in drilling operations for connecting together a series of tubular pipes incorporates an adequate combination of pressure seals for ensuring maximum sealing integrity at all times. In addition, none of the known prior art devices are as effective and reliable as the present construction and none utilizes a sealing arrangement which is not easily destroyed or neutralized by damage or other defects arising during storage, normal field handling, stabbing and running operations, or any other drilling activity.